(1) Field of the Invention
Fertilizer materials derived primarily from urea with other additional useful additives and plant nutrient materials are treated with a buffered solution of N-(n-butyl) thiophosphoric triamide (NBPT) dissolved in a mixture of one or more amino alcohols with one or more carboxylic acids having 6 or fewer carbon atoms to reduce nitrogen volatilization. The solution may be applied as a coating for granular urea fertilizers, or mixed with an aqueous fertilizer solution.
(2) Description of the Prior Art
The degradation of urea to release ammonia when applied to the soil is well known. The losses of applied nitrogen due to volatilization can be substantial (see review by Terman “Volatilization Losses of Nitrogen as Ammonia from Surface Applied Fertilizers, Organic Amendments and Crop Residues” in Advances in Agronomy 31: 189-223, 1979). The losses of nitrogen from urea applied to the soil are dependent upon a number of factors including: soil pH, soil temperature, soil moisture, cation exchange capacity of the soil and soil organic matter content. Greater losses of nitrogen from urea are observed as the soil temperature increases, as the soil pH increases and as the organic matter content increases. Decreased nitrogen losses of nitrogen from urea are observed whenever the soil moisture is high. In addition the depth of fertilizer placement influences nitrogen losses and surface placements are generally subject to greater nitrogen loss. The relative humidity at time of fertilization can influence losses. Recent rainfall events will tend to reduce losses if sufficient water is present to distribute the fertilizer into the soil.
Methods for controlling volatile nitrogen loses from urea have included the application of metal salts of copper and zinc, boron compounds, organic urease inhibitors, acid coatings, polymer coatings, and reaction of urea with aldehydes to form a slow release molecular adduct (see background in Whitehurst. et. al. U.S. Pat. No. 6,830,603 which is incorporated by reference). A number of extended release products have been proposed to help control volatile nitrogen losses.
N-(n-butyl)-thiopsosphoric triamide (NBPT) is a known urease inhibitor described by (Kolc et. al. U.S. Pat. No. 4,530,714). The compound is a waxy solid with poor water solubility making it difficult to coat urea and achieve adhesion of the compound. The compound undergoes hydrolysis and is thermally unstable.
The 714 patent describes the mixing of NBPT with organic solvents (acetone, disobutylketone, methanol, ethanol, 2-propanol, ether (diethyl), tolune, methylene chloride) to distribute the compound into the soil in an effective concentration range which can be anywhere from 5 ppm to 100 ppm depending upon the soil. The organic solvents described by the 714 patent are either too flammable for use or pose significant health risks to be considered suitable for coating urea granules.
In an alternate method, the 714 patent indicates that NBPT can be mixed with solids such as gypsum or clay to distribute the compound into the soil in an effective concentration.
Omilinsky et. al. (U.S. Pat. No. 5,698,003) describes the dissolution of NBPT with a glycol such as propylene glycol or ethylene glycol and esters of glycols. Glycols are compounds with adjacent alcohol groups in the chemical structure. The dissolution may contain a co-solvent liquid amide such as N-methyl-2-pyrrolidine and potentially a surfactant or dispersing agent such as polyethylene glycol or esters of polyethylene glycol (polyether alcohols). The patent indicates that esters of glycerol (a triol) may be used as the base solvent. Urea granules containing NBPT are prepared by mixing the urea granules with the NBPT dissolution solvent. Omilinsky et. al. teach that a drying agent such as clay or gypsum may be added to the compositions in the event that a product with excessive wetness is obtained.
Weston et. al (U.S. Pat. Nos. 5,352,265 and 5,364,438) teach the dissolution of NBPT in liquid amides such as 2-pyrrolidone or N-alkyl-2-pyrrolidones such as N-methyl-2-pyrrolidone to prepare both solid urea formulations (265 patent) or liquid formulations (438 patent).
Hojjatie et. al. (US 2006/0185411) teach the use of a number of sulfur salts of calcium or magnesium (calcium polysulfide, thiosulfate, magnesium thiosulfate) as urease inhibitors to prepare granular or liquid urea compositions.
Quin (US 2004/0163434) teaches the formation of a sulfur coated urea which may contain the urease inhibitor NBPT supplied from a proprietary liquid formulation sold as Agrotain® and distributed by Agrotain International LLC, Indiana, USA.
Sutton et. al. (U.S. Pat. No. 5,024,689) teach the formation of a liquid fertilizer that includes urease inhibitors such as NBPT and nitrification inhibitors such as dicyandiamide in aqueous mixtures of urea ammonium polyphosphate, ammonium thiosulfate and potentially other plant growth improving compounds.
Sutton (US 2007/0295047) teaches the formation of a solid fertilizer comprised of urea and a urea-formaldehyde polymer which may additionally include a urease inhibitor such as NBPT.
Sutton et. al. (US 2007/0157689) describes a fertilizer additive composed of urea, a urea-formaldehyde polymer and NBPT dissolved in an N-alkyl-2-pyrrolidone.
Urea is a high nitrogen analysis material which is often desirable as a starting material for making additional fertilizer products providing phosphorus or potassium as primary nutrients, calcium, magnesium or sulfur as secondary nutrients or micronutrients such as boron, copper, iron, manganese, molybdenum and zinc.
Whitehurst et. al. (603 patent) describe a coating methodology wherein a boron containing urease inhibitor composition may be used to add additional nutrients such as phosphate, potassium, etc. The coating of urea with other materials is known and the references in Whitehurst et. al. (603 patent) provides a partial summary of prior art in the area. The inhibitors and binders of this invention are aqueous mixtures that include ethanolamine borates, diethanolamine borates or triethanolamine borates and mixtures of these.
Commercial products containing aqueous ethanolamine borates or triethanolamine borates are distributed under the trade name of ARBORITE® by Encee Chemical Sales, North Carolina, USA. The product is further identified by a binder number for separation of the different mixtures available.